36412266951domain: NAppears in sequencesa(0)=1 if n>0 a(n)=(-1)^(n+1)/(2n+1) * Sum_{k=0..n} 4^(5k)*B(2k)*C(2n+1,2k) where B(k) denotes the k-th Bernoulli number.at n=4A076573